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USING BENLATE: Some lessons learned • A fungicide having both protective • With repeated use, resistance can • Fungicides having similar modes of and curative/systemic activity can provide effective disease control at low rates (ounces/acre). occur very rapidly. • Combining fungicides having dif- action can result in fungi having cross-resistance. ferent modes of action can reduce the risk of economic losses and potentially delay the selection for resistant fungal strains. SOURCE: David Ritchie, North Carolina State University Lessons from Benlate Dr. David Ritchie, plant pathologist at North Carolina State University, told stone fruit growers at the Great Lakes Expo that, back in 1972, the introduction of the new fungicide Benlate changed what growers expected a fungicide to do. But it also taught them unexpected lessons on deal- ing with emergence of fungicide-resistant diseases. Unlike the protectant fungicides in use before then, benomyl provided control of multiple diseases and was taken up and moved systemically within the plant, meaning that wash-off was less important and that disease control could be achieved for unsprayed parts of the plant, Ritchie said. Furthermore, it had protec- tive and postinfection activity, and was highly effective at ounces rather than the pounds of product per acre required for other fungicides such as sulfur and captan. But another characteristic became its Achilles' heel: benomyl had a site-specific mode of action. Following three consecutive years of exclusive use of Benlate on cherries from 1973 to 1975, brown rot control failed, he said. It was found that strains of the fun- gus had become resistant to the fungicide and that there was cross resistance to other fungicides with a similar mode of action. There was the realization that, like the earlier experience entomologists had with insect resistance to DDT, plant pathologists would now have to deal with the prospect of pathogens becoming resistant to fungicides. After benomyl, chemical companies and growers became involved in a contin- ual search for new fungicides that would replace those that became ineffective after repeated spray applications. Benomyl was followed by the sterol biosynthesis inhibitors (SIs), which also include the DMIs Orbit (propiconazole), Indar (fenbuconazole), and Elite (tebu- conazole), and now their generics. Then came the dicarboximides like Rovral (iprodione) and Ronilan (vinclo- zolin). These were followed in the 1990s by the strobilurins [Abound (azoxys- www.goodfruit.com Apples Defend Your Orchard With PHEROCON® Attract Both Female And Male Codling Moths. PHEROCON® II B Trap Pears mating-disruptedconventional Lock In Your Investment With PHEROCON® Walnuts PHEROCON® VI Trap CM-DA COMBO.™ The Best Codling Moth Trapping System. For more information call 1-866-785-1313 or visit our website: www.trece.com Your Edge – And Ours – Is Knowledge. ® INCORPORATED INSECT PHEROMONE & KAIROMONE SYSTEMS CM-DA COMBO.™ codling moth, Lock In On Females… trobin), Flint (trifloxystrobin), and Gem (trifloxystrobin)]. All of these were prone to resistance development. After some years of discussion about whether fungicides of different modes of action should be tank mixtures or alter- nated sprays, or a combination, along came Pristine, the first of the packaged premixtures. • GOOD FRUIT GROWER FEBRUARY 15, 2012 29 G o F or T he P air